The present invention relates to a multiple-coordinate measurement sensor which comprises a low-friction, low-wear, torsionally-rigid kinematic system moveable in at least two and preferably three principal directions x, y and z.
Federal Republic of Germany Patent 22 42 355 (U.S. Pat. No. 3,869,799) describes a multiple-coordinate sensor in which the sensor head comprises a torsionally resistant succession of play-free, friction-free linear guide systems which may consist, for instance, of leaf-spring parallelograms. The disclosure of this and all other prior art materials mentioned herein is incorporated by reference.
This sensor has several disadvantages. The linear guide systems are connected in series, one after the other. Thus, the linear guide system which lies closest to the sensor reference base, in the case of a multiple-coordinate sensor which operates in three directions, must bear the weight of the following two guide systems, including their length-measuring systems and possibly zero-point and contact-force generators, and including the sensor-pin carrier and the sensor pins. The second guide system which follows the first guide system only bears the weight of the third guide system and its length-measurement system and possibly zero-point and contact-force generator, and the sensor-pin carrier and the sensor pins. The third guide system bears only the weight of the sensor-pin carrier and sensor pins. As a result of the different weights, greatly different static forces and moments must be borne or compensated by the corresponding linear guide system, and strongly varying dynamic forces and moments occur upon the accelerating and braking of the sensor.
Given these factors, the degree of rigidity and sagging of the individual guide systems differ very greatly, so that, in the final analysis, the respective degrees of uncertainty of the measurements made by the multiple-coordinate sensor in the three directions vary to at least some extent according to the direction. These difficulties arise, in particular, in a situation in which all the linear guide systems deflect simultaneously, for example, when scanning the surfaces of an object to be measured which lie obliquely to all of the guide axes, or in the case of measurements which are carried out very rapidly. They arise in particular when three-dimensional surfaces are contacted continuously, and at the same time, the measurement instrument and the measurement scanner are in continuous movement in all three axes ("scanning").
Due to the unfavorable weight distribution of this known multiple-coordinate sensor, the latter also cannot, in practice, be used in different positions in space. Forces and moments would occur which could only be compensated for with difficulty.
This known sensor also has the disadvantage that all the cables and lines associated with the second and third linear guide systems must, in each case, be conducted through the first and second linear guide systems because of the connection of the linear guide systems in series. Friction and hysteresis are thereby introduced into the system, further increasing the uncertainty of the measurement. The deforming of the lines upon deflection of the linear guide systems can, furthermore, lead to a cable break.
A multicoordinated scanner is disclosed in DE-OS 37 25 205-A1 (U.S. Pat. No. 4,882,848). The articulated elements in that reference, however, are arranged in series and not in parallel.
A serial device for positioning an article with respect to two coordinate axes is disclosed in U.S. Pat. No. 3,377,111.
U.S. Pat. No. 2,932,482 discloses a mounting system for articles which consists of a parallel array of serially structured positioning systems. The positioning systems allow not only three linear degrees of freedom but also two rotations. The parallel combination of serial positioning systems is accordingly necessary to suppress these rotations.
U.S. Pat. No. 4,805,543 discloses another device for positioning an object, consisting of a parallel array of two or three sliding guides. In this device the sliding guides disadvantageously must be non-rotatable, which is not a requirement in the present invention. The reference also discloses leaf-spring parallelograms which are different from and cannot suggest the invention disclosed and claimed herein. In the case of the invention, each leaf spring element corresponds to an element in another line of the three guide systems. Hence the number of spring elements can be reduced to half the number of leaf spring elements in the reference. The device also lacks any compensation for the weight of the kinematic system, and lacks length-measurement and zero-point determining devices. The latter are usable in the present invention for performing measurements, which is not done by the device in the reference.